GTA:SA Duping FAQ

Duping stands for the Duplication of a Mission, which means starting several instances of the same Mission on top of eachother. This is used to complete the same mission twice (while really only doing it once), which for the game looks like the next mission in that line of missions has been completed as well, effectively skipping it.

Note: I know this FAQ is pretty long, it's just that even leaving out a lot of the details there is still quite a bit to Duping. Just scroll through the page and read whatever sections interest you.

Duping Basics

How do you start several missions at once?

Duping is all about making the game think that you're not on a mission, even though you are. The game tracks whether you're on a mission with the so called OnMission variable (which is just a number that's stored in the game's memory). OnMission is set to 1 when a mission is started and set to 0 when a mission is ended, causing mission markers (among other things) to be disabled or enabled accordingly. Phonecalls act just like a mission in this regard, setting OnMission to 1 when the phone rings, and to 0 when you end the call.

Some side missions (like Quarry, Blood Bowl or Bike School) can be started together with a phonecall (if timed correctly so you receive the call during the initial fade to black), so you end up with the phone ringing and a mission started at the same time, which normally is impossible.

Ending that "Setup Mission" will then set OnMission to 0, while the phonecall is still active, resulting in the so called "OnMission=0" call (read "On Mission Zero"). Ordinarily you can't start missions while a call is active, but with an OnMission=0 call you can, and can thus perform a Dupe:

• Start the mission you want to dupe, which sets OnMission to 1 (preventing you from starting any more missions)
• End the OnMission=0 call, which sets OnMission back to 0 (allowing you to start missions again)
• Start the same mission a second time

What does "Holding" a call mean?

Keeping an OnMission=0 call active is essential for Duping, however there are a lot of things that would simply cancel the call, for example shooting, entering a vehicle or ending missions. Holding a call means holding down the "Answer Call" button (called "Action" in the settings), which basicially keeps the call "On Hold". In this "About to answer" state, the call can be held active through all of the aforementioned activities (as long as the button is held).

Holding the call in a vehicle requires you to hold "Secondary Fire", which internally maps to the same function as "Action" ("Answer Call") does on foot. This is probably due to this being a console port, where both these functions are on the same physical button (in some versions at least). If you don't want to mess around with two buttons at once, you can bind both "Action" (On Foot) and "Secondary Fire" (Vehicles) to the same button and then use that for holding calls. (More Information on holding calls..)

Note that opening any menu (like saving), scoping with a weapon (like Sniper Rifle) and probably also some cutscenes will drop the call.

Carrying an OnMission=0 call through a mission

Sometimes it's faster to do a Duping Setup a few missions before the actual Dupe (for example to reduce travelling). Even though holding a call can keep an OnMission=0 call active through a lot of things, it's often impossible to carry it through a whole mission. Instead, the mission is being done on OnMission=0 itself:

• Start a mission with an OnMission=0 call (gained from a Setup Mission)
• End the OnMission=0 call, setting OnMission to 0 (without starting the mission a second time)
• Before completing the mission, receive another call and hold it
• Complete the mission with the held call, setting OnMission to 0 (giving you the OnMission=0 call back)

You can think of it like this: Initially, you use the vulnerability of the Setup Mission to get a call and a mission running at the same time, so you can fail the mission and get an OnMission=0 call. With that call you can then phonecall start any mission, and either do a dupe or just leave it on OnMission=0 to be able to again receive a call while on a mission, getting an OnMission=0 call when the mission concludes.

Being on a mission with OnMission=0 also allows you to save the game, which is sometimes used during the run to advance the time or get rid of the wanted level (although since there is a mission running, loading that save would crash the game). Getting OnMission=0 during a mission is also used for the 0* Glitch (see Woozie Skip below).

What is this awful screen flickering? D:

It's called Pause Buffering, which is basicially just holding down the ESC-button to quickly pause and unpause the game. In regards to Duping, this is used quite often to make the phone ring faster, in order to receive the call on time when starting a Setup Mission. During the fraction of a second fade you have to receive the call in, you can advance the phone timer by several seconds using Pause Buffering. In most cases this simply makes the timing a lot easier, but for some types of phonecalls it's actually required to make it consistent in the first place.

Why did you randomly stop on the way to Blood Bowl?

Some Setup Missions require you to time the phonecall to ring right after entering the marker. When you receive and then cancel a call, the phone will ring again after about 15s (or 60s for some types of calls), allowing you to time it correctly. This is often done on the way to the Setup Mission, so that the time until the phone rings again can be used travelling instead of just standing around.

Effects of Duping

Skipping Missions

Each chain of missions in the game has a variable attached to it, which keeps track of how many of these missions you've already completed. For example CASINO_TOTAL_PASSED_MISSIONS increases everytime you complete a Casino mission in Las Venturas. It starts out at 0, so when you enter the appropriate mission marker for the first time, the game sees that you completed 0 Casino missions and thus starts the first mission. After you completed that mission, the counter gets increased to 1, so the next time you enter the marker the game sees that you've already completed 1 Casino mission and thus starts the second mission.

When you dupe a mission, it means that two mission instances are running at the same time (you can kind of think of a mission instance as some small program that runs within the game and controls what the missions does). Once you complete the duped mission, the part of the code that increases the variable CASINO_TOTAL_PASSED_MISSIONS (keeping with the example) is executed twice, so it increases the variable twice, which for the game looks exactly as if you passed two missions.

For example when complete the mission "Fish in a Barrel" the CASINO_TOTAL_PASSED_MISSIONS variable is increased once, making the next mission "Freefall" (as normal). However if you dupe "Fish in a Barrel" it is instead increased twice, which means the next mission is "Saint Mark's Bistro", skipping "Freefall".

Why is there no traffic?

When you dupe a mission inside a cutscene (so start the second instance while the cutscene of the first instance is running, which works because CJ is still standing in the mission marker, even if you can't see it) the effects of the cutscene can carry over, one of which being that traffic is disabled. If the cutscene took place in an interior you also get strange interior lighting during the mission.

He's walking around in a cutscene, what is this sorcery? D:

An OnMission=0 call, which is used for Duping, can give you access to phonecalls during a mission, which otherwise wouldn't be possible. If you receive a call, hold it and then end it during a cutscene it gives you back control over CJ, because ending a call usually means you should be able to fully control CJ again.

Duping Caveats

Why don't you skip half the game with Duping?

• Not all missions can be successfully completed when duped (it can softlock the mission or make the game crash).
• The setup time can be relatively long, so only some longer missions are worth to skip this way.
• At some points in the game (like Los Santos) a consistent Duping Setup simply hasn't been found yet.
• Some missions can't be skipped, because completing them unlocks important things other than increasing a variable.
• What a dupe skips depends on how the missions are grouped together into mission chains: Some missions, like the first of a chain, cannot be skipped at all with this method, since there is no mission before that to do twice. And even if a mission can be duped, it doesn't necessarily do anything useful, like the last mission of a chain, where there is no mission after that to be skipped. (Click for a collection of mission chains on the wiki..)

Why not just dupe one mission 10 times?

Duping requires you to start a Setup Mission to get an OnMisison=0 call, which usually can only be done when there isn't already a mission running (otherwise the game crashes), so most missions can only be duped once. The Quarry sidemission (which is only completed in 100%) can be duped several times because it is also a Setup Mission itself.

Specific Dupes

So what missions are actually duped?

The following Dupes are done in the current any% route including Woozie Skip and Gang Territories Skip:

• Jizzy (Cutscene) (skips Jizzy)
• T-Bone Mendez (skips Mike Toreno)
• Toreno's Last Flight (skips Yay Ka-Boom-Boom, and thus all SF Woozie missions) [Woozie Skip]
  • Skips: Mountain Cloud Boys, Ran Fa Li, Lure, Amphibious Assault, The Da Nang Thang
• Monster (skips Highjack)
• Flight School (skips N.O.E.)
• Fish in a Barrel (skips Freefall)
• Black Project (skips Green Goo)
• Beat Down on BDup (skips Grove4Life)
• Los Desperados (skips End of the Line Part 1, and thus all Gang Territories, except those in missions) [GT Skip]

It's difficult to tell how much time these dupes save altogether, but certainly over 30 minutes (this obviously also depends on how fast/slow you are or would be on the mission that is being skipped and how well the Duping itself goes).

Other missions that were/are commonly duped when using other (older) routes:

• Ran Fa Li (skips Lure)
• Amphibious Assault (skips The Da Nang Thang)
• Highjack (skips Interdiction)
• Verdant Meadows (skips N.O.E.)

Woozie Skip

A big change in the Duping Route was the Woozie Skip. When you dupe Toreno's Last Flight it skips Yay Ka-Boom-Boom, which is really important because Yay Ka-Boom-Boom is the only mission that requires all the Woozie missions to be completed, so if you skip Yay Ka-Boom-Boom you also skip that requirement, and thus don't have to do any Woozie missions in San Fierro.

The downside is that Yay Ka-Boom-Boom unlocks the Las Venturas (LV) area, so if you skip that, the bridges stay blocked and you get a permanent 4* wanted level when you continue with the LV missions. The 0* glitch can be used to get around the 4* wanted level.

Permanent 0* Glitch

The game has that feature where you can go to an airport and buy a plane ticket to another city. If you start that flight while Vigilante is running (with OnMission=0) you can regain control before the flight ends and blow up the plane before it reaches it's target position. That way the flight doesn't end properly and the game thinks you're still in that plane cutscene, which keeps the wanted level disabled permanently (the stars basicially get removed over and over again, which means they can sometimes flash up for a fraction of second).

One issue with this is that dying or loading a save removes the permanent 0* glitch.

Gang Territory (GT) Skip

The last mission in the game - End of the Line - actually consists of three separate missions, to allow for checkpoint technology. When you do Los Desperados twice (previous mission), it skips End of the Line Part 1, which is the only mission part that checks that you own a certain number of Gang Territories. So skipping Part 1 means you skip all Gang Territories (except the few ones during missions).

The issue with Los Desperados is that trying to complete it when duped will fail one of the instances, making the whole effort pointless. Skipping Gang Territories saves a lot of time though, so instead of duping Los Desperados it is done twice in a row. This requires some very exact timing, making it one of the harder Dupes in the game.

How to do Los Desperados twice in a row

Normally you can't do a mission twice in a row, since completing the mission increases the counter and the game would just start the following mission the next time you enter the marker. That and the fact that only one instance of Los Desperados is allowed to run at the same time results in the following stipulations:

• You have to start the second instance before the first is completed (so the counter is still at Los Desperados)
• You have to start the second instance after the the first is completed (so they won't be running at the same time)

This sounds impossible, however the way this game starts missions is that there is a distinct "mission starter thread", which is sort of an endless loop that continously checks if CJ is standing in the marker (among other requirements) and then decides which mission to start (based on the count of already completed missions). It then performs a short fade to black, until it finally starts the actual mission instance. This means that the mission is set on track to be started a fraction of a second before the actual mission instance is started.

To satisfy the above requirements, the first instance has to complete during the initial fade of the second instance (or rather of the mission starter thread about to start the second instance). This means entering the mission marker just before the first instance completes, which is achieved by:

• Starting the first instance with an OnMission=0 call, setting OnMission to 0 during the mission
• Attaching a satchel to the last enemy in order to remotely complete the mission (normally you wouldn't be next to the mission marker)
• Using a phonecall to regain control during the cutscene, and CJs house to prevent getting teleported to the cutscene location
• Using the cutscene dialog and a timing method to activate the mission marker at just the right time

Driving Skill and Driving School

The Gang Territory Skip requires you to use the Stadium in Los Santos for getting an OnMission=0 call, and the Stadium requires you to have at least 200 Driving Skill. Just driving around also gives you Driving Skill, but it's not quite enough, so you have to get 2-4 Golds in Driving School, each one giving 30 Driving Skill.

Other Categories

Why does 100% only have Quarry Duping?

For 100% runs everything that gives you Percentage has to be completed. The Percentage for Quarry is only awarded once you complete all Quarry missions, so Duping can be used to basicially do all missions at the same time. In regards to Percentage, duping Quarry is sort of like doing one big mission faster, rather than skipping missions.

Quarry Duping is also a bit special, because it can be duped several times, due to it also being a Duping Setup mission and it not crashing when starting it more than twice.

Detailed Explanations

https://kb.speeddemosarchive.com/Grand_Theft_Auto:_San_Andreas/Game_Mechanics_and_Glitches/Duping
https://kb.speeddemosarchive.com/Grand_Theft_Auto:_San_Andreas/Missions/Dupes